Currently live television delivered over IP networks uses one of two quite different networking technologies: one based on multicast and the other based on unicast. With multicast transmission, a single multicast stream carrying the content is pushed from a content server to multiple network nodes simultaneously, with those network nodes duplicating the content and forwarding to any subsequent nodes or clients as required. With unicast transmission, multiple streams of content are pulled from the server, one for each device consuming the content, typically using HTTP over TCP and Adaptive Bit Rate technology.
Multicast makes efficient use of the network when delivering the same content at the same time to many end devices, but often requires continual allocation of network resources regardless of the amount of viewing. In addition, many end devices such as some tablets and smartphones, do not currently support multicast.
Unicast suffers from sending multiple copies of the same content through the network, but requires no usage-independent allocation of network resources. Moreover, unicast is capable of delivering to all end devices, even in the presence of low or variable network throughput to the end device, which is a frequent occurrence for devices connected by wireless technology for example.
US patent application 2013/0024582 describes a system and method for dynamically switching between unicast and multicast delivery of media content in response to changes in concurrent demand for access to the media content. Furthermore, sequence numbers included in the video frames are used to align between unicast and multicast stream content.